search-channel.java

import java.nio.CharBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.StandardCharsets;

public List<String> searchChannel() {
    CharsetDecoder decoder = StandardCharsets.UTF_8.newDecoder();
    final FileChannel channel = new FileInputStream(pathFile).getChannel();
    MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
    CharBuffer decodedBuffer = decoder.decode(buffer);

    String[] a = decodedBuffer.toString().split("\n");
    List<String> found = new ArrayList<>();
    for (String s : a) {
        if (s.contains(SEARCH_TOKEN)) {
            found.add(s);
        }
    }
    return found;
}

related to medium article https://gae-piaz.medium.com/search-string-in-file-with-java-as-fast-as-possible-fedafdc7a3ee